The FRAMES project is developing a system for video database search, content-based retrieval, and virtual video program synthesis. For dynamic synthesis applications, a video program is specified at a high level using a virtual video prescription. The prescription is a document specifying the video structure, including specifications for generating associative chains of video components. Association specifications are sent to an association engine during video synthesis. User selection of a virtual video prescription together with the default behavior of the prescription interpreter and the association engine define a tree structured search of specifications, queries, and video data components. This tree structure supports generic user interaction functions that either modify the traversal path across this tree structure, or modify the actual tree structure dynamically during video synthesis.